This invention relates to the system for analyzing a vehicle state such as fuel consumption rate, and its analysis method.
JP-A-2000-205925 published by the Japanese Patent Office in 2000 discloses a fuel cost-performance display device which computes a fuel consumption amount based on a fuel injection pulse signal output from an engine control unit, computes a running distance based on a vehicle speed pulse signal output from a vehicle speed sensor, and computes and displays a fuel consumption rate by dividing the computed running distance by the fuel consumption amount.
However, the aforesaid device uses a fuel injection pulse signal for the computation of the fuel consumption rate, i.e., it assumes a vehicle equipped with an electronic fuel injection device (EGI), and cannot be applied to a non-EGI vehicle or a diesel engine which does not have a fuel injection pulse signal.
A method exists for computing a fuel consumption rate of a non-EGI vehicle or a diesel engine, wherein a BSFC (brake specific fuel consumption) is calculated by looking up an engine performance map which specifies the relation between running conditions such as the engine rotation speed and the brake specific fuel consumption, and computing the fuel consumption based thereon. However, normally such a map is not available, and even if it is, it is difficult to acquire. Also, if the device is fitted later by a retail shop, it must be adapted to various types of vehicle from different manufacturers, and it is practically almost impossible to prepare such engine performance maps individually for every vehicle.
It is therefore an object of this invention to make it possible to precisely compute fuel consumption rate without using a fuel injection pulse signal in a system for analyzing vehicle states. It is a further object of this invention to provide a subjective evaluation criterion of vehicle state by displaying a vehicle state including fuel consumption rate to a driver or manager.
In order to achieve above object, this invention provides a vehicle state analysis system for a vehicle with an engine, comprising means for estimating a brake specific fuel consumption under remaining running conditions based on generic brake specific fuel consumption characteristic data and a known actual brake specific fuel consumption under a certain running condition of the engine, and for generating an engine performance map which specifies the relation between the running conditions and the brake specific fuel consumption, means for computing the brake specific fuel consumption of the engine by looking up the engine performance map based on the running conditions of the vehicle being analyzed, means for computing a fuel consumption amount from the computed brake specific fuel consumption and engine output, and means for computing the fuel consumption rate from the computed fuel consumption amount and vehicle running distance.
Therefore, according to this invention, the engine performance map which specifies the relation between the running state (accelerator depression amount and engine rotation speed, or throttle opening and engine rotation speed) and the brake specific fuel consumption (BSFC), is automatically generated based on previously prepared generic BSFC characteristic data and the actual BSFC under a certain running condition of the engine to the analyzed. BSFC characteristic data is data showing how the BSFC varies according to the running conditions, and it is the ratio of the BSFC under other running conditions to the BSFC under a certain running condition (for example, the running condition under which the BSFC is a minimum) which is stored. In the analysis, the BSFC is calculated by looking up the generated engine performance map, and the fuel consumption amount and fuel consumption rate are computed thereupon.
The reason why the engine performance map can be automatically generated is that the BSFC characteristics are approximately independent of the engine type, so if generic BSFC characteristics which show how the BSFC varies according to running conditions, and the actual BSFC under a certain running condition are known, all the BSFC under the remaining running conditions may be estimated based on this actual BSFC.
Moreover, as the BSFC characteristics are effectively identical in engines having similar torque parameters, if several BSFC characteristic data are provided corresponding to representative torque parameters, and the BSFC characteristic data is selected from the engine torque parameters of the vehicle being analyzed, any engine performance map can be generated more accurately, and the current computational precision of fuel consumption rate can be further enhanced.
Also, if an optimum BSFC acquired from a catalogue or the like is used as the actual BSFC which serves as a reference when the BSFC is estimated under various running conditions, it is unnecessary to measure the actual BSFC for each type of vehicle.
Therefore, as the analysis system according to this invention does not require a fuel injection pulse signal for the computation of fuel consumption rate, the fuel consumption rate may be calculated in a non-EGI vehicle or vehicle with a diesel engine which do not have a fuel injection pulse signal, and the method can be applied to the analysis of the vehicle running states of all types of vehicles. Further, as the engine performance map can be automatically generated from pre-prepared BSFC characteristic data and data extracted from a catalogue, there is no need to provide an engine performance map for various types of vehicle from different automobile manufacturers, and the generality of the analysis system is enhanced.
The detail as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.